LED has many characteristics, such as slim, lightweight, power-saving and the like, hence is widely used nowadays. It mainly includes multiple layers made of semiconductor materials and stacked by epitaxy. Take a blue light LED as an example, it mainly consists of GaN-based epitaxy films.
Please refer to FIG. 1 for a conventional vertical LED. It is a sandwich structure including an N-type semiconductor layer 1, a light emitting layer 2, and a P-type semiconductor layer 3. Beneath the P-type semiconductor layer 3, there are in this order by stacking, a mirror layer 4, a buffer layer 5, a bonding layer 6, a silicon substrate 7 and a P-type electrode 8. The surface of the N-type semiconductor layer 1 can be treated in a roughening process to increase light extraction efficiency. An N-type electrode 9 also is disposed thereon. When a voltage is applied to the N-type electrode 9 and P-type electrode 8, the N-type semiconductor layer 1 provides electrons while the P-type semiconductor layer 3 provides electron holes. The electrons and the electron holes are recombined to generate light.
The N-type electrode 9 usually is formed on the N-type semiconductor layer 1 through a thin film manufacturing process. Because the contact area is in inverse proportion to the contact impedance, thus a smaller contact area produces greater impedance. Moreover, because materials generally selected for the N-type electrode 9 and the N-type semiconductor layer 1 cannot provide preferable adhesion between them to result in insufficient bonding strength, the N-type electrode 9 is easily to be peeled off from the N-type semiconductor layer 1 to cause damage of the LED.